Sensory Systems Flashcards
a stronger stimulus will give a greater amplitude or frequency
greater frequency
a longer stimulus will give greater length of signal or greater frequency
greater length
which primary afferent fibres signal is fastest
a-beta -thickest and myelinated
what do a-beta fibres receive
touch, pressure, vibration and proprioception
what do a-delta fibres receive
cold, fast pain and pressure
what do c fibres receive
warmth and slow pain
which of the 3 fibre types is the biggest and most myelinated
a-beta (hence fastest signal)
which fibre is unmyelinated
c fibres (hence slowest signal)
which two types mediate pressure
a-delta and a-beta
which two types mediate proprioception
a-alpha and a-beta
what is the dorsal root ganglion equivalent in the head
cranial nerve ganglia (nuclei)
the area a nerve is responsive to stimulus over is its _______ field
receptive
a nerve will _____ to send a AP
depolarise
a deeper receptor is more/less accurate
less accurate
what are the 3 types of primary afferent fibres of cutaneous sensation
A-beta, A-delta and C
what are the 2 types of primary afferent fibres of proprioceptin
A-alpha and A-beta
what types of sensory nerves that we know about are A-alpha or A-beta
muscle spindles and golgi tendons as in stretch and inverse stretch reflexes
afferent fibres of pain
A-delta and C fibres
how do all primary afferent fibres enter the spinal cord
through the dorsal root ganglion (or cranial nerve ganglia in head)
how do A-alpha and A-beta fibres travel up the spinal cord
they go up the dorsal column, synapse with 2nd order which then cross the midline and project up to the thalamus and so on
how do A-delta and C fibres travel up the spinal cord
they are thermo and nociceotive so they synapse and cross over at entry and travel in the spinothalamic tract
where does all the sensory information terminate
somatosensory cortex (postcentral gyrus)
what happens when a stimulus is held for a long time
they APs stop. they will fire again when the stimulus is removed (like wearing clothes)
what pathway feature may explain referred pain
convergence
convergence increases/reduces acuity
reduces
when you touch an area of skin what is the effect on the surround nerve endings that are not being touched
they receive lateral inhibition
benefit of lateral inhibition
gives a sharper cleaner sensory image and borders are more defined
explain the gate control theory of pain
when A-alpha/beta neurons are excited and enter the spinal cord they stimulate inhibitory interneurones that release opioids (endorphins) to act on the A-delta/C neurones
when the original signals reach the midbrain this inhibition is further stimulated
effect of prostaglandins on bradykinin and thus on pain
prostaglandins sensitise nociceptors to bradykinin.
bradykinin is released in response to noxious stimuli which stimulates nociceptors.
prostaglandins therefore help pain signals be sent
when is bradykinin released
when there is a noxious stimulus
how do NSAIDs work to block pain
they inhibit cyclo-oxygenase enzyme (which generates prostaglandins) and so desensitise the nociceptor to bradykinin
local anaesthetic block which electrolyte responsible for action potentials
Na+ - all axonal transmission is blocked
how does TENS work
it stimulates mechanoreceptors at same level as pain and so stimulates the inhibitory opioid pathways blocking 1st to 2nd order neuron synapse
what class of analgesics activate descending inhibitory pathways
opiates e.g. morphine
what class of analgesics blocks transmitter release in dorsal horn when given epidurally
opiates e.g. morphine
which classes of analgesics reduces nociceptor sensitivity
opiates and NSAIDs
